1. Field of the Invention
The present invention relates to the field of rotary stencil printer, and more particularly to a device for mounting a leading end of a stencil to the printing drum of a rotary stencil printer.
2. Description of the Prior Art
The stencil printer has now reached a stage of full automatic rotary stencil printer in which the supply of a stencil, perforation thereof, mounting of the perforated stencil to the printing drum, printing and exhausting of the used stencil from the printing drum are all automated such that all those processes of the stencil printing are automatically carried out according to light instructions such as touching a push button by a tip of a finger. A proto-type of the basic construction of such a full automatic rotary stencil printer is disclosed in Japanese Patent Laid-open Publications 59-96983 and 59-143679.
In such a full automatic rotary stencil printer, a sheet to make a stencil is supplied as a band sheet coiled in a role and a predetermined length of the sheet to be mounted around the printing drum is cut out from the band sheet when each one stencil is produced. The leading end of the stencil is mounted to the printing drum by a stencil leading end mounting device comprising a base member having a band surface extending along a portion of a cylindrical outer surface of the printing drum in parallel with a central axis thereof for supporting the leading end of the stencil thereon, and a clamp member having a clamping surface and movable between a closed position where the clamping surface is laid over the stencil leading end supporting surface and an open position where the clamping surface is removed from the stencil leading end supporting surface. In such a stencil leading end mounting device, a most basic construction generally thought of as the clamp member, which, as described above, has a clamping surface and movable between a closed position where the clamping surface is laid over the stencil leading end supporting surface and an open position where the clamping surface is removed from the stencil leading end supporting surface, will be a flat band plate member, and a most basic construction generally thought of as a construction for mounting such a plate member to the printing drum to be movable between the above-described closed and open positions will be to support the band plate member along one of its opposite longer edges by a pivot shaft. In the embodiments of the rotary stencil printer disclosed in the above-mentioned Japanese Patent Laid-open Publications 59-96983 and 59-143679, the stencil leading end mounting device has such a construction.
However, there is a serious problem with respect to the above-mentioned construction of the stencil leading end mounting device of the full automatic rotary stencil printer. As will be understood from the figures of the above-mentioned publications, since the full automatic rotary stencil printer of this type includes three units such as a printing drum, a stencil supply means for supplying a new stencil to the printing drum and a stencil exhausting means for removing and exhausting the used stencil from the printing drum, if these three units are arranged in harmony within as small a space as possible, as a matter of course, the stencil supply means will be placed on one side of the printing drum, while the stencil exhausting means will be place on the other side of the printing drum. In such an arrangement, as viewed from the stencil leading end mounting device the leading end of a new stencil for the mounting approaches thereto from one side thereof, while the leading end of a used stencil is transferred as removed therefrom toward the other side thereof where the stencil exhausting means is positioned. Therefore, when the stencil leading end mounting device has the above-mentioned most basic construction, having a band plate member pivotably mounted along a longer edge thereof to the base member, the plate member may conveniently be inclined at an acute angle toward the stencil supply means like opening a mouth to be ready for receiving the leading end of a new stencil for mounting. In this case, however, it becomes difficult to let the leading end of the used stencil released from the clamping by the plate member proceed beyond the plate member toward the opposite side thereof for exhausting the stencil. Particularly when the used stencil is peeled off from the printing drum starting at the leading end thereof by a tip of a stencil removal claw being engaged into between the outer circumferential surface of the printing drum and the leading end of the stencil, while the printing drum is rotated in the same rotational direction as in the printing operation, as described in the above-mentioned Japanese Patent Laid-open Publications 59-96983 and 59-143679, although such a stencil removal process is desirable for removing the stencil adhered to the outer circumferential surface of the printing drum by the stickiness of the ink, it is important, for such a stencil removal process to be carried out with no problem, that the leading end of the stencil to be exhausted can move beyond the stencil leading end mounting device toward the opposite side thereof, and further that the stencil removal claw does not interfere with the stencil leading end mounting device when it traverses the front of the stencil leading end mounting device during the rotation of the printing drum for the exhaustion of the used stencil.
In view of the above-mentioned two requirements, it was proposed in Japanese Patent Laid-open Publication 59-96984 that, in a stencil leading end mounting device of the above-mentioned basic construction, the clamp member formed as a band plate element is turned from the closed position where one side of the clamp member is laid over the stencil leading end supporting surface of the base member to the open position for about 180.degree.. When a band plate element is turned over for about 180.degree. between the closed and open positions thereof, the movement of the leading end of a new stencil onto the stencil leading end supporting surface of the base member from one side thereof and the movement of the leading end of the stencil away from the stencil leading end supporting surface for exhausting the stencil toward to other side of the stencil leading end supporting surface are both unobstructed, and it is also avoided that the clamp member interferes with the stencil removal claw arranged to position its tip end desirably as close to the outer circumferential surface of the printing drum as possible, provided that the turn over of the clamp member for the approximate 180.degree. is completed before the printing drum is rotated in the same direction as in the printing operation for removing the used stencil therefrom.
However, when the band plate member is turned over for about 180.degree. between the closed and open positions as in the above-mentioned Japanese Patent Laid-open Publication 59-96984, a special space of a semi circular cross section corresponding to the turn over passage of the clamp member must be left vacant only for the turn over of the clamp member such that no other member interferes with the turn over of the clamp member, particularly at a special portion where it is desired that various other members are positioned, thus imposing an undesirable restriction against the compactness of the construction of the stencil printer.